1. Field of the Invention
The present invention relates to an optical unit installed within an image forming apparatus so as to expose a photoconductor to the light reflected from the original to form an image of variable magnification.
2. Description of the Prior Art
In an exposure process in a copying machine light is emitted from a light source to an original set on a platen made of transparent glass. The light reflected from the original is further reflected in the direction opposite to scan by a first mirror moving together with the light source as one unit in a direction to scan, further reflected through an upper second mirror and a lower third mirror in a direction to scan, after which the light reflected from the third mirror is guided through a lens to be reflected in the direction opposite to scan by a mirror unit comprising an upper fourth mirror and a lower fifth mirror. Finally, a photoconductor is exposed to the reflected light by a reflecting mirror provided in the optical path of this reflection light.
In such a copying machine, the change in a copy magnification, i.e., variable power is performed by reciprocating the lens and the mirror unit mentioned above in the direction to scan and the opposite direction thereto mentioned above.
FIG. 3 and FIG. 4 show one example of mirror units of this kind. A fourth mirror 10 and a fifth mirror 11 are contained in a mirror case 13 to compose a mirror unit 1. This mirror unit 1 is disposed on an optical bench plate 2 so that the mirror unit may reciprocate in the direction shown by the arrow D and the direction opposite thereto. This movement is performed by sliding a slide portion 14 provided on the longitudinal edge of the mirror case 13, and the movement of the slide portion 14 is guided by a slide guide shaft 15.
When a mirror unit 1 having such a structure is installed in a copying machine and carried, if a shock is inflicted on the mirror unit 1, the mirror unit 1 is likely to move, thereby spoiling the installation accuracy thereof, or causing troubles such as breakage. Then, in the conventional example mentioned above, when carrying the unit, the mirror case 13 and a metal fitting 16 provided at the position of the optical bench plate 2 facing the back of the mirror case 13 are fastened by a screw 17, which prevents the mirror unit 1 from moving while being carried, thereby protecting the mirror unit 1.
However, the conventional method for protecting the mirror unit mentioned above has required a complicated process for fastening a screw in a final finishing process in the production of a copying machine on the part of manufacturers, which has hampered the improvement of productivity.
On the other hand, there has also been required a process for releasing the screw when a copying machine is installed on the part of users. However, since the screw-fastening portion presents within a copying machine, the process for releasing the screw must be achieved with the outer case of the copying machine dismantled, which has caused a deficiency that a long period of time is required for the installation thereof.